Charged particle pulse accelerator incorporating a tesla coil



June 17, 1969 E. A. ABRAMYAN ET AL 3,450,996

CHARGED PARTICLE PULSE ACCELERATOR INCORPORATING A TESLA COIL Filed March 1, 1967 Sheet of s June 17, 1969 ABRAMYAN ET AL 3,450,996

CHARGED PARTICLE PULSE ACCELERATOR INCORPORATING A TESLA COIL Filed March 1. 1967, Sheet 2 of s FIE.

June 17, 1969 E. A. ABRAMYAN ET AL 3,450,996

CHARGED PARTICLE PULSE ACCELERATOR INCORPORATING'A TESLA COIL Filed March 1, 1967 1 u a z L U2 z 0 A f\ 6 C gt Z a [\0 Z U 6 [g F P 0T a? if F Z c c I c Sheet 3 of3 United States Patent US. Cl. 328-233 3 Claims ABSTRACT OF THE DISCLOSURE A charged particle pulse accelerator which incorporates a Tesla coil as the high voltage generator. A control electrode is introduced into the injector and a breaker of the primary winding for providing a considerably increased coupling coeflicient between the windings due to some structural modifications made therein.

This invention relates to installations for accelerating charged particles to energies of up to several mev., wherein use is made of an impact-excited resonance transformer (Tesla coil).

The prior art direct-voltage accelerations, which incorporate a Tesla coil as the high-voltage generator (cf. G. Breit, M. A. Tuve, and O. Dahl, A Laboratory Method of Producing Potential, Phys. Rev., 35, 51, 1930), display the following characteristic features, Charged particle acceleration proceeds as long as an accelerating voltage is available; the primary and the secondary windings of the transformer exhibit weak loop coupling, and every switching on of the commutator in the transformer primary winding causes the entire energy stored in the capacitor of this circuit, less the energy expended for accelerating the charged particles, to be lost in the form of heat in the transformer (Joule losses).

The disadvantages of the known accelerators are: a significant time-dependent scatter of the energy of charged particles; the impossibility of producing high pulse currents of charged particles since much of the energy stored in the primary circuit is carried away with the beam; low efilciency of the Tesla coil, i.e., the low ratio of the energy, delivered to the secondary circuit capacitor, to the energy stored in the primary circuit, and, hence, low overall efiiciency of the accelerators.

It is an object of the present invention to provide a simple and compact charged particle accelerator that will be noted for its high efliciency and operation reliability, and will render possible the production of charged particle currents of up to several hundred amperes at an energy of a few mev., and the pulse duration in the range of 10 to 10 sec.

It is the specific object of the present invention to considerably increase the coupling coeflicient between the primary and the secondary winding of the impact-excited resonance transformer, to increase the distributed capacity of the transformer secondary winding, and to provide current control in the accelerator.

This object of the present invention has been accomplished by a direct-voltage charged particle accelerator, which comprises disposed in the accelerator body, a Tesla coil, an electrode for the uniform distribution of high potential between the Tesla coil secondary winding and the accelerator body, and an acceleration tube disposed inside the secondary winding of the Tesla coil, wherein, according to the invention, provision is made for an open conducting screen, located between the primary and the 3,450,996 Patented June 17, 1969 secondary winding of the Tesla coil, and a control grid, disposed close to the acceleration tube injector, said grid being triggered once the maximum voltage is attained on the secondary winding of the Tesla coil, while the electrode for the uniform distribution of high potential between the high-voltage end of the Tesla coil secondary winding and the accelerator body is made permeable to variable magnetic flux.

The electrode for uniform distribution of high potential may be made in the form of a dielectric framework Wound with insulated wire, whose turns are electrically coupled with one another.

The invention is illustrated hereinbelow by an exemplary embodiment thereof and appended drawings, wherein:

FIG. 1 is a schematic cross-sectional view of the accelerator according to the present invention;

FIGS. 2a and b show the electrode for the uniform distribution of high voltage, plan and side views;

FIG. 3 is an equivalent electric circuit of the accelerator;

FIG. 4, FIG. 5 and FIG. 6 are the voltage curves of the transformer secondary winding, the charged particle current curves, and control grid voltage curves for three different modes of accelerator operation; and

FIG. 7 illustrates the voltage curves of the transformer primary and secondary windings and the charged particle current curves when the accelerator operates in the energy recovery mode.

The charged particle accelerator comprises a body 1 (FIG. 1), which houses a Tesla coil consisting of a coaxial primary winding 2 and secondary winding 3, and a magnetic conductor 4, which increases the Q-factor of the system and also the coupling coeflicient. Disposed close to the primary winding 2 and between the latter and the secondary winding 3 is an open conducting screen 5, which makes for the uniformity of the electric field in the vicinity of the primary winding and determines, thanks to the skin-effect, the direction of magnetic field lines. The screen may be employed as a turn of the primary winding 2. The Tesla coil may be insulated by means of pressurized gas, oil, or vacuum.

The high-voltage end of the secondary winding 3 is connected to an electrode 6, which is made permeable to variable magnetic flux and serves for distributing uniformly the high potential between said winding and body 1 of the accelerator. Good loop coupling of the windings and a nearly uniform distribution of voltage among the turns of the secondary winding 3 are obtained thanks to the fact that the insulating gap between the transformer windings is at a minimum because of the availability of the opening conducting screen 5 and also thanks to the possibility of magnetic flux passage through the electrode 6 of the secondary winding 3.

Disposed inside the secondary winding 3 is an acceleration vacuum tube 7, in whose upper part provision is made for an injector 8 and a control grid 9.

Where the secondary winding 3 or the entire transformer is contained in vacuum, the acceleration of charged particles may be effected without recourse to the acceleration tube.

Use can be made of various techniques for feeding power on the injector 8 and anarrangement (not shown) intended for control over the grid 9 of the acceleration tube 7, with said arrangement being mounted at the highvoltage end of the secondary winding 3 under the electrode 6. Power may be supplied, for example, via the secondary winding, within which case said winding is wound with two parallel wires, voltage from an external source being applied between said wires.

Voltage is fed to the primary winding 2 via a lead-in 10. A sleeve 11 serves as a beam outlet, while a sleeve 12 is intended for evacuating the acceleration tube 7.

Shown in FIG. 2 is the electrode for the uniform distribution of high potential between the Tesla coil secondary and the accelerator body. The electrode is made as a dielectric framework 13, onto which is tightly wound a winding 14 made from insulated wire, with the wire diameter being selected to conform with the skin layer thickness and the magnitude of permissible losses due to heating by eddy currents.

Thanks to the employment of a jumper 15 to connect separate turns of the winding, the equipotential surface of the electrode formed by the wire causes electric charges to be distributed uniformly.

The equivalent electric circuit of the accelerator comprises a primary winding 16 (FIG. 3), a secondary winding 17, a capacitor 18, distributed capacitance 19 of the secondary winding, a controlled commutator 20 through which the capacitor 18 is discharged into the primary winding 16 of the transformer, a rectifier 21, and an acceleration tube 22 provided with an injector 23 and a control grid 24.

Once the capacitor 18 is charged from the rectifier 21, the controllable commutator 20 is switched on, and there arise oscillations in the coupled circuits consisting of the primary winding 16 and the secondary winding 17 as well as of the capacitor 18 and distributed capacitance 19. The circuit parameters are selected so as to obtain equal natural frequencies in the circuits.

During oscillations, the secondary voltage U grows (FIGS. 4a, 5a, and 6a), while there occurs a concomitant decrease of the primary voltage. Then the situation is reversed, and the secondary voltage diminishes, while the primary voltage grows.

The acceleration tube injector is closed at all times, except for a time interval 1- (FIGS. 4b, 5b, and 6b) when the charged particle current flows through the acceleration tube.

The accelerator can be operated on different modes whose characteristics are presented in FIGS. 4a, b and c, 511, b and c, and 6a, b and c.

The first mode of operation involves triggering the grid of the acceleration tube for a short period of time 1' (FIG. 4c). The current i flowing through the acceleration tube (FIG. 4b) is preset by the permissible increment AU; of the accelerating potential during the burst time, 1.e.,

1 wherein C is the distributed capacitance of the transformer secondary.

In the second mode of operation (FIGS. 5a, b and c), the control grid is triggered for a longer period of time 1 3 /3 T, wherein T is the period of natural oscillations of the secondary winding. The later mode is expedient where it is desired to obtain a higher average power and the allowable particle energy variation in the beam equals 5 to 10%.

It is feasible to produce a wide current burst of the particles accelerated to constant energy by varying, according to a preset program, the current i in the acceleration tube within a time interval of T (FIGS. 6a, b and c).

In order to obtain a high efiiciency of the accelerator, particularly in the case of the short burst mode of control .4 grid operation (FIGS. 4a, b and c), recourse may be had to recovering the energy that remains in the secondary circuit, incorporating the secondary winding 17 and distributed capacitance 19, after passage of the current burst of accelerated charged particles.

At the time t (FIGS. 7a and b) the total energy left in the secondary circuit after passage of the charged particle current i will be stored in the capacitor 18' of the primary circuit, so that current in said circuit will equal zero.

When at this moment of time, use is made of the controllable commutator 20 to break the primary circuit, the oscillations will discontinue and, on recharging the capacitor 18 by means of the rectifier 21 to obtain the initial voltage U the accelerator will be brought to the initial state. Hence, the energy lost is confined to that expended in the course of one cycle on generation of the Joule heat.

We claim:

1. A direct-voltage charged particle accelerator which comprises: a body; a Tesla coil with a primary winding and a secondary winding and a magnetic conductor housed in said body; an open conducting screen disposed between said primary and secondary windings of the Tesla coil; an electrode for a uniform distribution of high potential between said Tesla coil secondary winding and the body, said electrode being made permeable to variable magnetic flux; an acceleration tube disposed inside said Tesla coil secondary winding and furnished with an injector and a control grid, with said grid being mounted close to said injector.

2. An accelerator according to claim 1, in which the electrode for a uniform distribution of high potential between said secondary winding of the Tesla coil and said body is a dielectric framework wound with insulated wire whose turns are electrically coupled with one another.

3. A direct-voltage charged particle accelerator which comprises: a body; a Tesla coil with a primary winding and a secondary winding and a magnetic conductor housed in said body; a controllable commutator incorporated in the circuit of the primary winding of said Tesla coil and intended for recovering the energy in said accelerator; an open conducting screen between said primary and secondary windings of the Tesla coil; an electrode for a uniform distribution of high potential between said Tesla coil secondary winding and the body, said electrode being made permeable to variable magnetic flux; an acceleration tube disposed inside said Tesla coil secondary winding and furnished with an injector and a control grid, with said grid being mounted close to said injector.

References Cited UNITED STATES PATENTS 2,578,908 12/1951 Turner 328233 2,695,374 11/1954 Jeppson 313-63 X 2,939,086 5/1960 Westendorp 328233 JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

US. Cl. X.R. 

